Bug fixes and Plugin search fixed

- Changed PluginImporter to be static.
- PluginImporter no longer scans the manifests of all jars in a class
path. It now takes all plugins from a specific directory.
- Added folder structure to Jar Files.  This allows them to be
recognized as proper java classes.
- Fixed a bug in cleaning the test structure that only recreated the
head directory
- Added a non plugin sample class to test whether they get added to the
plugin list.